Approaching fully equiaxial grains of Er/Zr modified selective laser melted Al–Mg–Mn alloys

Abstract

In this study, high-strength Al-8.5Mg-0.78Mn-0.96Er-1.94Zr alloys are prepared by selective laser melting(SLM). The microstructure and mechanical properties of the Al–Mg–Mn–Er–Zr alloys in the as-built and heat-treated states are investigated. The results show that Al3(Er,Zr) primary phases with L12 structure (≤200 nm) formed during the SLM process. These phases act as heterogeneous nucleation sites and promote the formation of ultrafine equiaxial grains (0.3–0.85 μm) at the melt pool boundary. It inhibits the epitaxial growth of columnar grains, and equiaxial grains (2–6.45 μm) are formed in the melt pool center. Er and Zr have significant refining effects on the alloy, forming a nearly fully equiaxed grain structure. After the aging treatment, a large number of Al3(Er,Zr) precipitation phases with sizes of 2∼5 nm is diffusely precipitated, which promotes the precipitation strengthening. The tensile strength of the as-build sample is 521 MPa, the yield strength is 446 MPa, and the elongation is 14%. After the aging treatment, the yield strength increased, and the elongation decreased. Er/Zr-modified SLMed Al–Mg–Mn alloy can improve alloy properties, reduce costs, expand applications, and provide theoretical support for alloy design and processing.

Keywords

• Selective laser melting
• Ultrafine equiaxial grains
• Er/Zr addition
• Mechanical properties